Various processes and apparatuses are known for the production of straight bead welded tubes from strips and sheet metal blanks, but none of them make possible the economic manufacture in medium size runs of tubes having a relatively short length (for example, 1=3000 mm), a small diameter (for-example, d=50 mm) and a relatively large wall thickness (for example, t=2.5 mm). It is therefore an object of the invention to provide a process and an apparatus for the production of such tubes.
In the prior art process of roller shaping (U.S. Pat. No. 2,110,378) a strip is shaped in a number of successively arranged stages by driven profiled rollers to give a slotted tube which is then welded. The investment cost of an installation suitable for this purpose is very high, so that it is unsuitable for the production of tubes in medium size runs.
In the prior art 3-roller bending, a flat sheet metal blank with two supporting rollers is bent around a working roller. Such a process enables tubes to be produced with a wall thickness of, for example, 1.0 mm and a diameter of 50 mm only with a length of less than 2000 mm, since the supporting rollers sag due to the heavy supporting forces to be applied. There is also the aspect that the resulting slotted tube must be removed from the apparatus and straight bead welded at another place.
A clamping and retaining apparatus for relatively short slotted tubes is also known (DE 44 32 674 C1) in which the slotted tube is retained by bands, which are partially looped around the tube, in a suitable welding position for a welding device which can be driven along the joint gap. To obtain a straight bead welded tube, therefore, a sheet metal blank must be shaped into a slotted tube in a separate apparatus.
In another prior art apparatus (DE-PS 966 111) for the production of straight bead welded tubes from flat sheet metal blanks with parallel longitudinal edges, the sheet metal blank is shaped into a slotted tube in the same apparatus, being retained by the means shaping the tube with the longitudinal edges to be welded in the welding position. Two form tools disposed laterally inverted in relation to one another, which are borne by a tool support, can be driven towards one another, and have outer cylindrical half shells received in their opened receiving position the sheet metal blank at its two longitudinal edges. When the form tool halves are moved together, the sheet metal blank is retained at its two ends fixed in the center, so that the sheet metal blank slides along the cylindrical half shells on both sides until its longitudinal edges impinge on one another at the top point. The sheet metal blank shaped into a slotted tube is retained in this position. Then, to weld the longitudinal edges to one another, the top ends of the form tool halves can be hinged upwards, so that the joint gap is opened up. An important disadvantage of such an apparatus is that there is the risk that the sheet metal blank may bend outwards for lack of internal and external guiding. This risk is particularly great in the case of thin-walled sheet metal blanks.
In a very similar prior art apparatus for the shaping of sheet metal blanks into tubes, which are then welded (DE-PS 593 622) the two form tool halves are formed not by cylindrical half shells, but by axially offset discs with cutaway portions in the shape of arcs of a circle. The apparatus is to be used to form a conical tube from a sheet metal blank. To this end the disc cutaway portions in the shape of arcs of a circle increase in radius in the axial direction. However, in distinction from the other aforedescribed prior art apparatus, in this prior art apparatus an internal conical mandrel is associated with the outer parts of the form tool halves. However, the mandrel is not operative during the entire shaping operation, but only at the end thereof, since it is applied to the sheet metal in the center between the form tool halves. Due to the absence of internal and external guiding during the shaping operation, even the use of such a mandrel does not obviate the risk that the sheet metal blank will bend outwards during the shaping operation.
It is an object of the invention to provide a process and an apparatus which enable straight bead welded tubes to be produced from sheet metal blanks, more particularly blanks with a thin wall thickness. More particularly, the process and the apparatus are suitable for the processing of sheet metal blanks of different thicknesses, for example, so-called tailored blanks.
The invention therefore starts from a process for the production of a straight bead welded tube from a flat sheet metal blank having parallel longitudinal edges, wherein the sheet metal blank is shaped into a slotted tube by means of two form tool halves having outer cylindrical half shells and disposed laterally inverted in relation to one another which can be moved towards one another, whereafter the longitudinal edges are welded to one another at the top of the form tool, being retained in position by the form tool halves. In such a process according to the invention during shaping the sheet metal blank is borne on the inside by internal cylindrical mandrel halves co-operating with the outer half shells to produce form gaps, the longitudinal edges emerging at the top retaining exposed for welding (sic).
The invention also relates to an apparatus for the production of straight bead welded tubes from flat sheet metal blanks with parallel longitudinal edges having: form tool halves having outer cylindrical half shells and disposed laterally inverted in relation to one another which are borne by a tool support and can be moved towards one another and can be moved out of an opened receiving position for the sheet metal blank into a closed position, in which the longitudinal edges to be welded to one another are held together by the closed tool halves at their top point, the device also having a welding device which can be moved over the form tool halves along the longitudinal edges retained in the welding position. In such an apparatus the invention is characterized in that the form tool halves have cylindrical internal mandrel halves which are associatedly fixed with the outer half shells and which cooperate with the outer half shells to produce form gaps for the sheet metal blank to be inserted, while in the closed position of the form tool halves the form gaps retain the longitudinal edges emerging therefrom at the top exposed for welding.
The process according to the invention and the apparatus according to the invention enable sheet metal blanks of different thicknesses to be formed into a cylindrical tube without any risk that the blank will bend outwards during the shaping operation. More particularly, the invention enables short tubes to be economically produced in medium size runs from sheet metal blanks. Both tubes having a constant wall thickness can be produced, and also tubes which have differential wall thickness over their length or periphery. The special advantage of the invention is that the form tool halves themselves retain the shaped slotted tube with the joint gap in an optimum welding position, to produce the weld by the welding device movable along the joint gap. This means that two separate devices are no longer required for shaping and for retaining the slotted tube in the welding position. This also eliminates the laborious transfer of the slotted tube, with the necessary alignment and clamping.
In a first embodiment of the invention the sheet metal blank is first pushed by one half completely into one of the form gaps and then by its other half into the other form gap. One of the two form tool halves, more particularly the movable one, can have adjacent the entry to the form gap an abutment against which one longitudinal edge of the sheet metal blank can bear when the form tool halves are moved together. This gives the sheet metal blanks satisfactory guiding, making it impossible for the blank to be introduced at an angle into the form gap.
To improve the geometry of the joint gap, during or after its emergence from the form gap the sheet metal blank can be so after-shaped in narrow strips adjoining the longitudinal edges that they merge substantially tangentially into one another. With the apparatus this can be effected in two ways. Either a tool acting on the longitudinal edges in the sense of moving them together is associated with the top zone, or the form gaps terminate at the top in a common horizontal plane.
The required spatial fixation of the internal mandrel halves in the outer half shells with the possibility of being able to remove the shaped tube can, according to a further feature of the invention, be effected by the features that the outer half shell and the internal mandrel half of each form tool half are connected to one another at one of their ends, and the internal mandrel half is releasably located by its other end directly on the tool support, the internal mandrel half being otherwise retained in position by a number of supporting members which extend through the outer half shell via recesses and can be uncoupled via sliding couplings on the internal mandrel half in the direction of the outer half shell.
Constructionally this can be put into effect by the feature that the outer half shell and the internal mandrel half connected thereto at one end bear against one another without a gap in this connecting portion and are held together by releasable clamping elements. The result is a highly precise association between the half shell and the internal mandrel half with a very simple assembly. The releasable clamping elements enable the form gap to be somewhat opened, to pull the finished tube out of the form tool or even to pull the internal mandrel halves out of the finished tube.
To enable the tube to be pulled out of the form tool with the front end of the internal mandrel half released, without the internal mandrel half making it difficult to pull out the tube by bearing thereagainst, according to a feature of the invention the internal mandrel half projects in relation to the outer half shell at the connected end, and associated with the projecting portion is a pressure element via which a pivoting force around a horizontal transverse axis in the sense of relieving the front end of the internal mandrel half can be applied to the internal mandrel half.
To prevent the sheet metal blank from bending outwards when the blank is introduced into the form gaps, according to the invention a vertically adjustable supporting construction for the sheet metal blank to be introduced into the form gaps is provided immediately below and in the receiving position between the form tool halves. The supporting construction preferably has at the entrance of each form gap a deflecting plate extending over the entire length of the form gap and is borne resiliently in the direction in which the form tool halves move. The deflecting plates yield when on completion of shaping the form tool halves arrive in the closed position.
The precise positioning of the longitudinal edges at the top point of the form tool halves for straight bead welding can be ensured using simple means. According to one feature of the invention associated with one of the two form tool halves, more particularly the fixed one, is a retractable stop at the top for the longitudinal edge of the portion of the sheet metal blank shaped in said form tool half. The stop also then acts as a support when the sheet metal blank is inserted into the form gap of the other form tool half. Preferably the stop has a tip so asymmetrically constructed that when the other longitudinal edge impinges on said stop the stop yields, releasing one longitudinal edge, and both longitudinal edges impinge on one another, thus forming a butt joint.
To prevent dirt occurring during welding, such as splashes of melt or smoke (for example, evaporated zinc in the case of galvanized sheets) from dirtying the form tool, according to one feature of the invention an intercepting bowl is disposed in the zone of the top of the internal mandrel halves. Such an intercepting bowl can be cleaned or interchanged after each use of the welding device.
Preferably the intercepting bowl is disposedly fixed and extends over the entire length of the form tool halves. With such a construction also according to a possible feature of the invention the intercepting shell is connected tightly to the internal form halves and co-operates with the exposed longitudinal edge zones of the tube formed from the sheet metal blank to form a channel. Such a channel is suitable for protective gas flushing or for removing by suction the vapors occurring during welding.
Conveniently the intercepting bowl is made of a flexible material and has a V-shaped cross-section. This construction is particularly suitable, since it can readily adjoin the internal mandrel halves and does not impede the moving together of the form tool halves, since during this it folds together.
However, alternatively the intercepting bowl can be constructed to move together with the welding device. Constructionally this can readily be effected if according to the invention the intercepting bowl is borne at the end face by a tappet for the ejection of the internal mandrel halves.